“Midnight Cowboy and Easy Rider were both low-budget movies, both made $100 million and together they brought the whole studio system down,” stresses Michael Childers, Midnight Cowboy’s production assistant and on-set photographer. “The studios were freaking out: ‘How could these rebellious, outrageous X films about these lowlifes make all that money?’ More importantly, they both led the way with this New American Cinema that spawned some of the greatest movies ever made that certainly changed people’s attitudes, woke them up to reality and made cinema great again in what is now seen as a golden age of US movie making.”

Indeed, Midnight Cowboy, the first and only X-rated movie to win three Academy Awards (Best Picture for producer Jerome Hellman, Best Director for John Schlesinger and Best Adapted Screenplay for Waldo Salt, plus nominations for its three leads) certainly set the cougar among the canaries on its release in 1969 and, 50 years on, hasn’t lost any of its grime or grit. The film tells of the poignant relationship between two polar opposites: Joe Buck, a naive Texan cowboy (Jon Voight) who travels to New York with the intention of becoming a male prostitute specialising in rich, middle-aged ladies, and the decrepit and crippled New York small-time scam artist “Ratso” Rizzo (AKA Enrico Salvatore, played by Dustin Hoffman). A movie that is up there with the great pictures of the 20th century, it is at once experimental, enormously prescient and agonisingly tender.

“I’ve shown it at ten film festivals this year alone and I’d say that 70 per cent of the audiences had never seen it before,” attests Childers in the UK to help publicise the film’s 50th anniversary. “It really holds the audience’s attention; it gets the laughs, it gets the tears. It holds up incredibly well and hasn’t dated at all. I believe the reason for this is that it’s about the human condition, compassion and a greater humanity. What kept these two guys together was that they were both down and out and were bonded by misfortune and poverty. Ratso was dying and starving and the cowboy wanted to protect him and help him see his dream.

“When we were there in New York filming, Robert Kennedy and Martin Luther King were assassinated, Nixon was president and the Vietnam War was in full swing. People were taking to the streets; millions of people demonstrating. New York was in turmoil. It was bankrupt bother, morally and financially. The streets were falling apart; there were garbage strikes everywhere. It was a really extraordinary time and I think the film in many ways reflects that. It’s thrilling to see the audience’s reaction to it today after half a century. They are in awe.”

If the movie were French it would have been described as new wave, if Italian it would be neorealism and if British a kitchen sink drama. No surprise, then, that Hampstead-born Schlesinger was a pioneer of the latter. His first two features – A Kind Of Loving (1962) and Billy Liar (1963) – are jewels in the genre’s crown. Midnight Cowboy, however, as a piece of gut-wrenching social realism, is on another level. The story’s starving protagonists have lost everything – their dignity, their masculinity, their self-worth – and as such are struggling to remain on the lowest rung of the social ladder. Luckily, they find each other, not in a sexual respect, but in a way that can touch us all. They are simply friends who would do anything for each other no holds barred. If we are lucky enough we can empathise with that. Ergo, Midnight Cowboy is the ultimate “buddy movie”.

Undeniably, though, the term “buddy movie” hugely sells the picture short. It is also a film about America that puts the US under the microscope as only a non-American might. In essence it is a Pop Art movie, a social document that takes every opportunity to expose the eccentricities of America. Starting with Joe’s journey from Texas, we see the American travel bible belt and field after dull field. As the young would-be hustler drifts off into thought, Schlesinger uses flashbacks to dissect the American South even further – rodeos, evangelism and corporal punishment – so that, by the time our hero hits New York, the contrast slaps us mightily in the kisser.

Suddenly, Joe is in this crazy conurbation that, home to millions, is as barking as the Deep South. Neon, skyscrapers, homeless winos and cross-dressers, it is at once fascinating and intimidating for our youthful cowpoke who strolls the streets head and shoulders above the crowds dressed in his cowboy boots, hat, shirt and buckskin fringed jacket. Of course, Schlesinger doesn’t miss a trick in using Joe’s alienation to scrutinise New York City and its every more.

“Well, it’s like a documentary of America, warts and all,” smiles Childers, who was the director’s significant other for 30 years. “John [Schlesinger] was a documentary filmmaker in the Fifties. A lot of people forget that. He worked for the BBC. He did over 30 documentaries, one of which won the Berlin Film Festival, called Terminus, which helped start his career. But, yeah, he loved the strangeness of America. The strangers and the strangeness. Everything was new, exciting and crass, full of energy. He loved American energy. He and Ridley Scott were both Brits who really examined and MRI’d America in their movies.”

Throughout the picture, Schlesinger features lo-fi wooden television sets blasting out nonsense just to remind us how absolutely barking the US is: rapidly racing through the channels we see dogs in lingerie, bible-bashing lunatics, beauty shows, exercise routines, Godzilla and atrocities from Vietnam.

“That idea was so John Schlesinger,” says Childers, sniggering. ”In those days, the first remote controls were just coming out and he couldn’t get them to work at all. He’d get really mad at the TV sets and used to flip through all these crazy channels at breakneck speed shouting at the TV. But I think he secretly loved the craziness of US TV.”

It’s a valiant picture artistically, the director not holding back on experimental filmmaking techniques one iota. Some might compare this bravely renegade aspect to that of Performance, filmed at roughly the same time and directed by Donald Cammell and Nicolas Roeg. But its deft observation and subtle nuance lifts it to an altogether loftier plateau. Unlike many films that bung one too many spaced-out spanners in the works, Midnight Cowboy, based on the 1965 novel of the same name by James Leo Herlihy, perfectly balances narrative with art house. Dream sequences using black-and-white film, stills, wild editing and arcane effects do not detract from the story, but add to it. The movie’s party scene, perhaps the finest ever produced, is pure genius and so, so achingly New York.

“That was partly my idea,” says the 75-year-old Childers, chuckling. “I was friends with Paul Morrissey, who did all the Warhol movies and so was obviously close with Andy, and we’d hang out at Max’s Kansas City with him and Andy Warhol and The Velvet Underground crew, Debbie Harry, New York Dolls and all those crazy people. I brought John there for a couple of dinners with Paul, and one with Andy, and he was fascinated. I said, ‘Look! In the book it just says, ‘A party in Sue’s in Greenwich Village.’ ‘What’s that?’ I said, ‘Let’s turn it into something completely Warhol.’ I had all the superstars in it – Ultra Violet, International Velvet, Paul Jabara, Hollywood Blonde, Paul Morrissey, Joe D’Alessandro, Taylor Mead, Patti D’Arbanville and Andy really wanted to be in it. Problem was that he was shot the week before by Valerie Solanas and we had to start shooting.”

Said scene is like a short film within a film, Schlesinger filming the host (Gastone Rossilli) who himself films the outlandish guests who seem genuinely off their nuts writhing about half naked against a backdrop of Thirties projections. Using double exposures, staccato editing, strobes and oil lamps Schlesinger accentuates every barking turn of this crazy gathering that, juxtaposed against Joe and Rico’s naiveté, certainly emphasises their plight. It is a virtuoso ten minutes.

Lest we forget, none of this could ever have worked quite so well if it wasn’t for the bravura performances from the actors.

“All the leads were Oscar nominated – Sylvia Miles, Jon and Dustin – and I think they should have won,” stresses Childers, who was one of the founding photographers on Warhol’s Interview magazine. “Dustin was cast before they started filming. They saw him in a Broadway play and thought he was brilliant and very smartly signed him up before The Graduate came out. The Graduate came out as we started to shoot Midnight Cowboy and he became the biggest movie star in the world. We wouldn’t have been able to afford him after that! Jon Voight was not originally cast as the cowboy. Originally a Canadian heartthrob was cast as the cowboy. And then his studio, Universal Pictures, tripled his salary and we couldn't afford him any more. So we went back and looked at Jon Voight’s screen tests and said, ‘Holy shit!’ Voight was the best. Jon managed to convey naivety, confidence, anger and violence all at the same time. But all the cast were divine. Still, it was very difficult shoot. The unions in New York were a nightmare. They hated all the freaks, the drugs, the homosexuality and made it really difficult for us. But we got there in the end and we were all very proud of the end result.”

And then there’s the haunting soundtrack that, regarded as one of the all-time greats, was a must-have album in 1970.

“We were living down in a rental house in Malibu and somebody turned us on to Harry Nilsson,” Childers recalls. “Our neighbour down there was Bob Dylan. I loved Sad-Eyed Lady Of The Lowlands and John loved Everybody’s Talkin’, so we played it and played it, put it on the rough cut and we got so attached to it. We didn’t think we could afford Everybody’s Talkin’ but we spoke to Nilsson and he allowed us to use it. Thank God. It was perfect. And then Toots Thielemans played that beautiful mournful harmonica on the theme that John Barry wrote and the soundtrack album hit the charts. It was a pretty exciting time for us all.”

Luckily for fans of great film, Midnight Cowboy has been digitally restored and, to coincide with its 50th anniversary, is to be rereleased. One of the most daring and innovative films of the Sixties and Seventies, it is an astonishing achievement that cannot be missed on the big screen.